CNS Infections
Clinical Presentation Definitions *Meningitis - Inflammation of the meninges *Encephalitis - Inflammation of brain parenchyma *Brain abscess - Localised collection of infected material within the brain Acute Chronic Investigation Meningitis #CT ##Role of CT in meningitis is mainly for excluding space occupying lesion raised pressures/focal swelling/odema, hydrocephalus (determines whether lumbar puncture can be performed), not for diagnosis ###Suspect space occupying lesion if: ####Patient drowsy with focal neurological signs or seizures ####More likely that meningitis is of bacterial, not viral etiology ##Usually nothing will be picked up on CT ###The only sign might be diffuse leptomeningeal enhancement on CT/T1 contrast-enhanced MRIor hydrocephalus ###However, in TB meningitis CT reveals hydrocephalus, meningeal enhancement, intracranial tuberculoma #If CT does not reveal space occupying lesion, hydrocephalus or cerebral odema proceed with lumbar puncture + microbiology Notes: #Traumatic taps: ##RBC from traumatic taps can falsely elevate WBC counts ##Correct by the formula: WBC added = WBC(blood) x RBC(CSF) / RBC(blood) ##A useful guide (if serum WBC and RBC are normal): 750 RBC in CSF = 1 WBC in CSF #If CT reveals space occupying lesion, and other contraindications do not perform lumbar puncture Other Investigations: *FBC (WBC), ESR, Blood c/s, PCR *Throat swab Encephalitis #CT ##Role of CT is diagnostic ###HSV: low-density lesions in the temporal lobes ###CMV: paraventricles #Other investigations ##FBC (Tw), ESR, blood c/s and PCR ##EEG ##HSV: periodic epileitiform activity in temporal lobes Cerebral Abscess #CT ##Role of CT/mri is diagnostic ###Single or multiple low-density areas (indicate necrotic material) with ring enhancement (indicates surrounding edema) #Other investigations ##FBC (Tw), ESR, Blood c/s and PCR ##Look for the source of the abscess: US, CT (Lung, abdomen, etc) Management Antimicrobial treatment principles in CNS infection *CNS is an area with reduced host resistance *Treatment requires bactericidal therapy *For most drugs, CNS penetration is only about 10-20% Ask 4 questions *Where is the infection? **From outside to inside, the locations are: skin and subcutaneous, sub-galeal, skull (osteomyelitis), epidural abscess, subdural empyema, encephalitis, brain abscess *How long has it been going on? **acute- hours/days **subacute- weeks **chronic- months *What is the clinical setting and exposure history? **community acquired ***pneumococcal and meningococcal meningitis **hospital acquired ***MRSA and pseudomonas meningitis **age of the patient **sick contacts ***in closed environments like dormitories- meningococcus **sexual history ***unprotected sexual intercourse- HIV, neurosyphilis *Is the patient a normal or immunocompromised host? **In patients with compromised immune systems, organisms that do not usually cause infections can cause infections ***e.g. Toxoplasmosis in AIDS Manage according to location *Meningitis **Divide into acute and chronic **Divide into bacterial and viral using CSF parameters ***Bacterial ****Opening pressure 200-500, WBC 500-5000, predominantly neutrophils, glucose < 2.2, CSF:blood glucose < 0.4, protein 100-500 ****Community-acquired bacterial meningitis *****Admit and treat with IV antibiotics- vancomycin and 3rd-gen cephalosporin. Add ampicillin if over 50 years old ****Hospital-acquired *****Usually occurs days or months post neurosurgery or procedures like lumbar puncture *****Can either follow indolent or fulminant clinical course ******Indolent- skin commensals (Staphylococcus epidermidis) ******Fulminant- MRSA or gram-negatives like Pseudomonas *****Treat with IV antibiotics- vancomycin and 3rd gen cephalosporin. Add a penem (eg meropenem) if post-neurosurgery, shunt, or penetrating trauma ***Viral ****Opening pressure <250, WBC 50-1000, predominantly lymphocytes, glucose > 2.2, CSF:blood glucose > 0.6, protein < 200 ****Less sick, generally self-resolving. No specific treatment required except for fluids and analgesia *Encephalitis **General treatment measures ***anticonvulsants- prevent or treat seizures ***corticosteroids- reduce inflammation and swelling in the brain ***sedatives- for excessiveirritability ***paracetamol- for pain ***ventilator- life support ***fluids **Mostly viral etiology ***HSV-1 ****Most common ****Temporal lobe involvement on MRI, PCR good to use ****Is the only treatable viral encephalitis- if severe, admit and treat with acyclovir 10mg/kg IV q8hrs x 2-3/52 ***Arboviruses ****Mosquito vector ****Uncommon in Singapore ***Japanese Encephalitis virus ****Used to be endemic in Singapore but incidence dropped after abolition of pig farming in 1992 *Brain abscess **Spread from contiguous structures/post-op incision sites via veins (face, sinuses, ear infections) **Accompanied by focal neurological signs- e.g. paralysis, gait disturbance **Can be a medical emergency **Admit and treat aggressively **Empiric antibiotics- vancomycin + ceftriaxone + metronidazole (anaerobes) **Surgery indicated under the following conditions: (NB: if surgery is indicated, start antibiotics after drainage and collection of tissue for stains and culture) ***Persistent or progressive ICP ***Gas-containing mass ***Signs of impending abscess rupture into brain ventricles Done by: CG 28 2013/2014